Cities across southern and western states are issuing warnings and opening cooling centers ahead of a potentially dangerous heat wave expected to begin on Wednesday. Forecasts indicate that temperatures could soar above 110 degrees Fahrenheit in some areas, impacting at least 29 million people under heat alerts and warnings. These alerts cover regions from central California into Nevada and Arizona, and parts of southern Texas.

An area of high pressure is causing these unusually elevated temperatures, with daytime highs predicted to be 10 to 25 degrees above average across the affected areas. NBC meteorologist Angie Lassmann noted that several locations could post record temperatures on Friday.

San Angelo, Texas, reached 111 degrees on Tuesday, marking the city’s third hottest day ever, following a record of 112 degrees last year. The National Weather Service has indicated that California’s Central Valley could see temperatures "well up into the 100s at the hottest location," with interior desert regions, including Las Vegas, expected to experience heat around 110 degrees by Thursday.

Parts of California, Nevada, and Arizona are bracing for triple-digit temperatures as the first heat wave of the season hits. In California's Death Valley National Park, temperatures could reach between 118 and 121 degrees. Consequently, California has activated phase 2 of its extreme heat temperature response plan, mobilizing state agencies to address heat-related illnesses and prepare cooling centers.

"Extreme heat can be deadly. Together, let’s do everything we can to stay safe. The state is taking action to protect and inform communities and Californians should take steps now to protect themselves from the heat," said Governor Gavin Newsom in a statement.

Phoenix, Arizona, could see temperatures reach 110 degrees for the first time this year on Wednesday, slightly later than the city's average date of June 11 for such heat. The city is forecast to reach 113 degrees on Thursday, which would be its hottest day on record. Other cities are also likely to see heat records broken.

In Texas, San Antonio has opened 30 cooling centers for residents needing air conditioning. Similar centers are operational in Corpus Christi, Texas; San Jose, California; and Clark County, Nevada. Los Angeles County, the most populous county in the U.S., issued a heat warning for the Antelope Valley from Wednesday through Friday, advising residents to stay hydrated and avoid sun exposure.

Municipal leaders and first responders are grappling with the challenges posed by extreme heat, including finding effective methods and resources. Last year in Maricopa County, Arizona, which includes Phoenix, there were 645 heat-related deaths, exacerbated by a 31-day period of consecutive 110-degree temperatures.

Firefighters are now using ice submersion techniques, pioneered by the U.S. Army, to cool heatstroke victims. This involves placing patients inside a blue bag filled with ice during transport to the emergency room. This cold water immersion therapy, already used by local hospitals, will now be employed by Phoenix fire and paramedics personnel for every patient showing signs of heatstroke.

“Just last week, we had a critical patient that we were able to bring back before we walked through the emergency room doors,” Fire Capt. John Prato told The Associated Press. “That’s our goal — to improve patient survivability.”

Additionally, new projections indicate that the average cost of cooling a home from June to September will be 8% higher than last year, further straining resources as temperatures rise.

Authorities are also on high alert for fires in the region, with fire usage restrictions in place across central and western Arizona. A grass fire near Tracy, California, approximately 65 miles east of San Francisco, grew to more than 14,000 acres over the weekend.

The U.S. Border Patrol in El Paso, Texas, reported that four migrants attempting to enter the country illegally died of heatstroke and dehydration over the weekend. "We urge anyone considering crossing illegally to understand the severe risks involved. Our agents are working tirelessly to save lives. But the best way to stay safe is not to attempt an illegal crossing," said El Paso Sector Chief Patrol Agent Anthony S. Good in a statement.

As the heat wave progresses, communities across the affected regions are advised to take necessary precautions to stay safe and minimize the risks associated with extreme heat. This includes staying indoors during peak heat hours, hydrating regularly, and utilizing local cooling centers.